Breakaway oxidation behavior of Fe-based cylinder coating with eutectic ceramics in water vapor at 650 °C

In this study, we investigate the oxidation behavior of a Fe-based cylinder coating mixed with 35 wt% eutectic ceramic particles. About 250 μm thick coatings were produced on the cylinder surface by using internal rotating plasma spraying. The cylinder coatings were placed in an environment at 650 °C to experience air plus water vapor oxidation as well as air oxidation. In order to do the analysis, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), energy dispersive x-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used. The results show that after spraying, the Fe-based coating has less defects and a uniform and dense structure, in which Al2O3, Al2O3/ZrO2 and a small amount of ZrO2 are evenly distributed. In addition, Al2O3/ZrO2 ceramic particles play a certain role in delaying the breakaway oxidation in the following stage. The oxidation behavior of the Fe-base coating is obviously different from that of traditional alloys. The oxidation rate in the aqueous atmosphere is higher than that in the air. This is mainly reflected in the diffusion of elements, the formation and volatilization of oxides, and the formation and aggregation of pores, which therefore play important roles in the breakaway oxidation. The role of ceramic particles in the oxidation of coatings, the reasons for the high oxidation rate, and the breakaway oxidation mechanism of Fe-based coatings in water vapor were analyzed.